Method and Apparatus for Casting a Concrete Pile in the Ground

ABSTRACT

A concrete pile is cast in the ground by driving a plate into the earth with a tubular mandrel to create a shaft. Fluid grout injected into the mandrel can flow from the mandrel to fill the shaft. The plate is tethered to the mandrel and is recoverable for reuse when the mandrel is withdrawn from the grout filled shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/664,838, filed Jun. 27, 2012.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for casting a concrete pile in the ground and, more particularly, to a method and apparatus enabling recovery of the apparatus used for forming the shaft in which the pile is cast.

DeWitt, U.S. Pat. No. 4,992,002 and DeWitt, U.S. Pat. No. 6,773,208 disclose methods for economically producing concrete piles in the ground. A boot comprising a tube closed at one end by a plate is driven into the ground by a pile driver impacting a mandrel inserted into the tubular boot and bearing on the plate. The mandrel is a hollow tube with a diameter slightly smaller than the inside diameter of the boot and is filled with a fluid grout which can flow out of the mandrel through holes near the lower end of the mandrel. The grout flowing out of the mandrel under pressure fills the annular spaces between the exterior of the mandrel and walls of the boot and the hole or shaft produced by driving the boot into the earth. The presence of the grout between the mandrel and the wall of the shaft stabilizes the shaft wall helping to prevent soil from invading the grout column and maintain the diameter of the shaft as the shaft is driven deeper. In addition, the grout lubricates the mandrel reducing friction and focusing the pile driver's energy on the plate at the bottom of the boot. When the shaft has been driven to the appropriate depth, the mandrel is withdrawn from the boot and the shaft. As the mandrel is withdrawn, the grout injected into the mandrel under pressure can flow out of the open end of the mandrel filling the shaft. While these methods reduce material waste and facilitate economical production of piles with high load bearing capacity, the boot is abandoned when the mandrel is withdrawn increasing the cost of forming a pile.

What is desired, therefore, is a method and apparatus for producing a driven grout pile which enables recovery of the apparatus used to drive the shaft for the pile.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an end of a mandrel assembly used in producing a driven grout pile in the ground.

FIG. 2 is a cross-sectional elevation view showing the mandrel assembly of FIG. 1 during the process of forming a shaft for a concrete pile cast in the ground.

FIG. 3 is a cross-sectional elevation view showing the mandrel assembly of FIG. 1 during withdrawal from a shaft filled with grout.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A driven grout pile provides an economical alternative to other methods of pile construction. Referring in detail to the drawings where similar parts are identified by like reference numerals, and, more particularly to FIGS. 1 and 2, a driven grout pile is cast in the ground 20 by injecting a fluid grout 46 into a hole or shaft 22 produced by driving a mandrel assembly 24 into the ground with a pile driving apparatus and then continuing to fill the shaft with grout as the mandrel assembly is withdrawn from the grout filled shaft. The mandrel assembly 24 comprises a bottom plate 26 having an upper surface 28, an opposed lower surface 52 and a cross-sectional shape, often circular, and size matching the cross-sectional shape and size of the desired shaft. The bottom plate 26 is placed on the surface of the ground 20 at the desired location of the pile and an elongate tubular mandrel 30 is engaged with the upper surface 28. The mandrel comprises a wall defining an external surface and an internal surface enclosing a passage and preferably has an annular cross-section although the cross-section could have any desired shape. The cross-section of the mandrel is somewhat smaller than the cross-section of the bottom plate and, therefore, the cross-section of the shaft produced by driving the bottom plate into the ground. The mandrel is somewhat longer than the deepest pile which is to be formed with the mandrel. Located near the open end at the bottom of the mandrel are a plurality of grout openings 32 which will permit fluid grout in the interior passage 31 of the mandrel to flow through the wall of the mandrel. The upper end of the mandrel 30 is engaged with a pile driver (not shown) which supplies the energy to drive the mandrel assembly into the ground.

The mandrel assembly 24 also preferably includes a reaming device 34 slidably attached to the mandrel near the mandrel's lower end. The reaming device preferably includes a frusto-conical lower portion 36 having a base with a cross-section larger than the cross-section of the mandrel and only slightly smaller than the cross-sectional size of the bottom plate 26. The reaming device is longitudinally slidable on the mandrel and is preferably attached to the mandrel by a pin 38 or a bolt which fits in holes in the wall of the mandrel and which is slidable in elongate slots 40 in the reaming device. The wall of the reaming device 34 also includes a plurality of grout openings 42 which are arranged to align with the grout openings 32 in the mandrel 30 when the mandrel and the reaming device are both in contact with the top surface of the bottom plate. When the mandrel is lifted, the elongate slots 40 permit the reaming device 34 to slide longitudinally downward on the mandrel so that the grout openings 42 in the reaming device no longer align with the grout openings 32 in the mandrel blocking the openings through the wall of the mandrel.

The mandrel assembly 24 includes a locating feature which maintains the lateral position of the bottom plate relative to the mandrel during driving but which allows the mandrel to move vertically with respect to the bottom plate if it rebounds during driving and to separate from the mandrel when the mandrel is raised. The locating feature preferably comprises at least three pins 44 affixed to the top surface 28 of the bottom plate 26 and arranged so that the outer surfaces of the pins engage the inner surface of the tubular mandrel's wall when the end of the mandrel is in contact with the bottom plate. However, other features attached to the bottom plate and arranged to contact either the inner or outer surface of the mandrel or a surface of the reaming device could be used to releasably connect and maintain the lateral position of the bottom plate. On the other hand, features affixed to the mandrel or reaming device and engageable with surfaces, such as the edges of holes or slots, in the bottom plate could also function as the locating feature.

The bottom plate 26 is attached to the mandrel 30 by a tether 45, preferably a length of chain, which is preferably affixed to the mandrel proximate the longitudinal axis of the mandrel, for example by attachment to the center of the pin 38. The tether passes through a notch 54 in the ends of the mandrel 30 and the reaming device 34 and the second end of the tether is attached to the bottom plate 26 proximate its periphery. Referring also to FIG. 3, the tether 45 is of sufficient length to enable the bottom plate 26 to hang clear of the mandrel 30 and the reaming device 34 when they are lifted from the bottom plate.

To create a driven grout pile 60, the upper end of the mandrel 30 is connected to a pile driving apparatus (not shown). The bottom plate 26 is placed on the ground surface 20 at the location where the pile is to be cast and the lower end of the mandrel 30 and the reaming device 34 are lowered into contact with the upper surface 28 of the bottom plate. As the mandrel 30 is lowered onto the bottom plate the locating feature, pins 44, is engaged with the mandrel to laterally align the mandrel with the bottom plate.

The pile driving apparatus drives the mandrel 30, the reaming device 34 and the bottom plate 26 downward creating a hole or shaft 22 in the earth. When the shaft has reached sufficient depth to confine the flow of grout from the mandrel, liquid grout 46 from a source 50 is pumped into the interior 31 of the tubular mandrel through a hole 52 in the mandrel's wall proximate the upper end of the mandrel. Since the reaming device 34 is pushed upward by contact with the bottom plate, the grout holes 42 in the reaming device align with grout holes 32 in the mandrel allowing fluid grout to flow out of the mandrel into the annular space 48 between the outside surface of the mandrel and the wall of the shaft. Grout is injected into the mandrel under pressure as the driving continues and flows from the mandrel into the annular space to lubricate the mandrel and support the wall of the shaft maintaining the diameter of the shaft and resisting potential mixing of soil with the grout.

When the bottom plate 26 has been driven to the appropriate depth, the mandrel is lifted by the pile driving apparatus. As the mandrel 30 is lifted above the surface 28 of the bottom plate 26 the reaming device 34 slides downward on the mandrel misaligning the grout holes 42 in the reaming device and the grout holes 32 in the mandrel to block further flow of grout through the wall of the mandrel and prevent soil from being transported into the grout column. The fluid grout can continue to flow through the open end of the mandrel to fill the shaft 22 with grout as the mandrel is lifted. As the reaming device is moved upward by the mandrel, the frusto-conical portion 36 of the reaming device 34 presses outward on the grout in the annular space 48 around the mandrel compacting the soil in the wall of the shaft. After the mandrel 30 has been lifted sufficiently to tauten the tether 45, continued lifting of the mandrel raises the peripheral edge of the bottom plate 26 so the bottom plate hangs below longitudinal center of the mandrel with the opposed planar surfaces 28, 52 aligned substantially parallel with and approximately equal distance from the longitudinal axis of the mandrel minimizing the cross-section of the bottom plate exposed to the grout and reducing the likelihood of contact with the wall of the shaft as the bottom plate is withdrawn through grout column by the mandrel. If desired, a form may be set at the top of the grout column and filled with additional grout to raise the top of the pile above the adjacent surface when the mandrel and bottom plate have been withdrawn from the shaft and reinforcing bars are often driven into the fluid grout column. When the grout hardens, the cast-in-place concrete pile 60 is complete.

The mandrel 30, the reaming device 34 and the bottom plate 26 can be reused in producing additional piles reducing cost of concrete piles cast in the ground.

The detailed description, above, sets forth numerous specific details to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid obscuring the present invention.

All the references cited herein are incorporated by reference.

The terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow. 

1. An apparatus for creating a shaft in earth, said apparatus comprising: (a) a plate; (b) an elongate tubular mandrel having an end bearably engageable with a first surface of said plate, said mandrel arranged to urge said plate into the earth; and (c) a tether attached proximate a periphery of said first surface of said plate and affixed to said mandrel proximate a central longitudinal axis of said mandrel and arranged to support said plate with said first surface and a spaced apart second surface aligned approximately parallel to and spaced approximately equal distances from said longitudinal axis of said mandrel when lifted by said mandrel.
 2. (canceled)
 3. The apparatus of claim 1 wherein said tether comprises a flexible member.
 4. The apparatus of claim 1 wherein said tether comprises a chain.
 5. The apparatus of claim 1 further comprising a pin secured to said mandrel and arranged substantially normal to said longitudinal axis of said mandrel, said tether secured to said pin.
 6. The apparatus of claim 1 wherein said plate further comprises an aligning feature slidably engageable with said mandrel and operable to align said plate in directions normal to said longitudinal axis of said mandrel.
 7. The apparatus of claim 6 wherein said centering feature comprises plural pins affixed to said first surface of said plate and arranged for slidable engagement with an interior surface of said tubular mandrel when said end of said mandrel is bearably engaged with said plate.
 8. A method of creating an earthen shaft for a concrete pile comprising the steps of: (a) driving a plate into earth with an elongate tubular mandrel, said plate tethered to said mandrel by a tether having a first end connected to said mandrel proximate a longitudinal centerline of said mandrel and a second end connected proximate a periphery of a surface of said plate; and (b) withdrawing said mandrel and said plate from the resulting shaft. 9-10. (canceled)
 11. A method for creating a concrete pile in the earth comprising the steps of: (a) placing a plate on an earthen surface; (b) engaging a first surface of said plate with an end of an elongate tubular mandrel, said plate attached to said mandrel by a tether affixed proximate a longitudinal axis of said mandrel and at a periphery of said first surface of said plate; (c) driving said mandrel and said plate into the earth to create a shaft; (d) injecting a fluid grout into said tubular mandrel while driving said plate, said grout flowable into said shaft from said mandrel at a portion of a wall of said mandrel defining a grout passage proximate said end of said mandrel; and (e) withdrawing said mandrel and said plate from said shaft, grout in said mandrel flowing from said end of said mandrel as said mandrel is withdrawn.
 12. The method for creating a concrete pile of claim 11 further comprising the step of blocking said grout passage in said mandrel during withdrawal of said mandrel and said plate. 13-14. (canceled) 